Automatic spray guns are frequently used on manufacturing production lines for coating diverse articles. A spray gun may be mounted, for example, on an industrial robot located in a spray booth. While the workpiece is temporarily located in the spray booth, a robot controller executes a program for moving the spray gun along a predetermined a path spaced from the workpiece surface and for triggering the spray gun on and off at appropriate times to coat the workpiece.
When a spray gun is used on a programmable spray painting robot, finite control of both the air and the fluid must be established. A robot may move the spray gun, for example, at a normal speed of four feet per second. This converts to a spray gun movement of approximately 2.5 inches in 50 milliseconds. If fluid to the spray gun is controlled by a solenoid actuated trigger valve located at a considerable distance from the spray gun, long delays with accompanying long lead distances for triggering the spray gun are inherent in the system. The problem of lead distances and other problems can be eliminated by locating a solenoid actuated trigger valve which controls the delivery of coating fluid and a solenoid actuated air valve which controls the delivery of atomization air and pattern shaping air in or adjacent the spray gun.
Where separate valves are used, one for controlling atomization air and pattern shaping air and the other for controlling coating fluid, it is desirable to open the atomization and pattern shaping air valve prior to opening the fluid valve and to close the fluid valve prior to closing the atomization and pattern shaping air valve. This sequence assures proper atomization and a proper pattern to the leading and trailing edges of the atomized coating. Such a sequence is achieved in manual spray guns by the use of a manual trigger which sequentially opens the air valve and a fluid valve as the trigger is squeezed. When the trigger is released, the valves are closed in the reverse sequence. This operating sequence has not been performed automatically with two solenoid actuated valves located in the vicinity of the spray gun.